1. Field of the Art
The present invention relates to a serial-impact printing device having character fonts or type elements, for example on a daisy type wheel, wherein a carriage which carries printing means, including such a type wheel, is moved along a line of printing to bring a desired character into a predetermined printing position. The positioned character is impacted subsequently on a recording medium, whereby successive characters are printed, one character at a time.
2. Related Art Statement
Such a serial-impact printing device is versatile, in that it may be used as a printer for printing data which is transferred from an external input device via an input connector, and also as a typewriter for printing data while the data is entered through a keyboard connected thereto. In either case, the printer is operated in a normal printing mode or in a special printing mode. In the normal printing mode, the characters are printed in a normal fashion-by means of intermittent movements of the carriage to successive printing positions. In the special printing mode, the characters are boldface-printed or shadow-printed for accentuation, or vertical lines are scored as for tabulation.
This type of serial-impact printer starts a printing action only after the carriage has been positioned at the appropriate printing position, and therefore suffers difficulty in speeding the printing operation. More specifically described, when a character is printed at printing position "b" of FIG. 5, the carriage is moved from the preceding position "a" to the printing position "b" by a one-character spacing. As indicated by curves C1 and C2 in the figure, the carriage undergoes a transient vibrational movement around the printing position "b", whose amplitude is gradually reduced to zero, with a result of the carriage being finally positioned at the predetermined position "b". The printing means is inhibited from starting its printing action until the transient phenomenon is thoroughly removed, i.e., until a point of time "t4" is reached, whereat the impacting action against the sheet of paper is started by the printing means. Accordingly, the waiting time of the printing means reduces the printing efficiency or speed of the printer.
Various attempts have been made to speed up the printing speed, i.e., to increase the number of characters printable per unit time. An example of such attempts is disclosed in Japanese Patent Application which was laid open in 1983 under Publication No. 58-67484. In a serial printer proposed in this application, the rate of movement of the carriage and the actuation timing of the print hammer are variably controlled depending upon a distance of movement of the carriage.
When characters are printed on paper in a normal manner with intermittent movements of the carriage, the characters do not generally give an unpleasant impression or appearance to the readers, even though the characters are deviated from their normal printing positions by a distance less than one tenth of a character-to-character spacing. On the contrary, the readers are likely to feel displeased with boldfaced or shadowed characters or vertical scores even when the specially printed characters or vertical scores are deviated only a slight distance from their normal positions. Thus, even a small amount of deviation of the carriage from the predetermined positions will degrade the impression or appearance of the boldfaced or shadowed characters, or vertical lines, and thus lower the printing quality in the special printing mode.
In the case where the printing device is used as a typewriter, it is required to correct or erase sets of characters or words which have been erroneously entered and printed. If the characters to be corrected are deviated from their normal positions, it is impossible to achieve perfect erasure or neat correction or replacement of the characters. When the printing device is operated as a printer, characters are merely printed and the correction of the printed characters is not necessary and impossible. In this case, non-special, ordinary characters will not give an unpleasant impression on the readers, even if the printed characters are slightly deviated from their normal positions.
It will be understood that the length of waiting time of the printing means required for substantial removal of the transient vibrational movement of the carriage at each commanded printing position, will differ depending upon the specific printing modes, that is, whether the printing device is operated in the special-printing mode for effecting a special printing such as boldfaced printing, shadow printing and vertical scoring, and whether the printing device is operated in the typewriter mode or in the printer mode. Accordingly, the use of constant length of waiting time before starting the impacting action without regards to the specific printing modes will lower the overall printing efficiency or printing speed of the printing device.